It is well known to transmit a multiplicity of conversations along a single transmission link by digital techniques. This is achieved by periodic sampling of an analog signal, such as a voice signal, and transmitting the samples in digital form in place of the signals themselves. The Nyquist sampling theorem fixes the minimum sampling rate as twice the highest frequency of the signal being sampled.
One widely used technique for digital information transmission is PCM, i.e. pulse code modulation, whereby each sample is expressed in an 8 bit code. Various other types of coding for digital information transmission are also known and used. All of the conventional digital transmission techniques are characterized in that only a single sample relating to a single conversation is being transmitted at any one time. Therefore, using conventional technology, one can transmit 30 voice and 2 signalling channels over a single communications link.
There is described and claimed in applicant's pending Israel Patent Application No. 63117 an apparatus and method for transmission of information in digital form including apparatus for providing a plurality of signals coded into a multiplicity of digital code elements in accordance with a first modulation technique; and apparatus for providing a plurality of coded addresses for transmission, each of the coded addresses representing a digital code in accordance with a second modulation technique corresponding to a combination of code elements of individual ones of the plurality of signals.
The present invention seeks to provide a method and apparatus for transmission of voice signals which enables maximum benefit to be obtained from the technique of the aforesaid Israel Patent Application 63117. The technique and apparatus of the present invention is also applicable to transmission techniques other than that described in the aforesaid Israel Patent Application 63117.